There has been known a method for producing a silanol-group-containing polysiloxane, which is used as a coating agent or the like for producing, for example, an anti-reflection film, the method including polycondensation of a silicon compound, preferably a siloxane or silane having an Si-bound alkoxy group, in the presence of a polycondensation catalyst.
However, the silanol-group-containing-polysiloxane solution produced through the method has poor storage stability, even after inactivation or removal of the polycondensation catalyst. Specifically, in some cases, the molecular weight of the silanol-group-containing polysiloxane gradually increases. Thus, due to such poor storage stability, storage or transport of the silanol-group-containing-polysiloxane solution may be considerably impeded.
Some methods are known for stabilizing a silanol-group-containing-polysiloxane solution by means of an additive, or modification of the solvent. In one specific method, an alcohol is added before or during polymerization to form a siloxane polymer, to thereby stabilize the viscosity of the siloxane polymer (see Patent Document 1). In another disclosed method, a polar solvent having a small polarization degree and a dielectric constant falling within a specific range is used, to thereby provide a composition containing an organopolysiloxane resin having a silanol group. The composition does not undergo condensation at room temperature, has remarkably excellent storage stability, and does not deteriorate over time (see Patent Document 2). However, through use of an additive (Patent Document 1) or modification of the solvent (Patent Document 2), the produced silanol-group-containing-polysiloxane solution has poor storage stability. Therefore, there is demand for another way of stabilizing the polysiloxane solution.
There is also disclosed a technique for producing a silicon-containing solution whose gelation is suppressed or prevented. This technique employs a hydrous H-type cation exchange resin serving as a catalyst of hydrolyzation and condensation of alkoxysilane (see Patent Document 3). Since the technique disclosed in Patent Document 3 employs a hydrous H-type cation exchange resin serving as a catalyst of polycondensation of alkoxysilane, the silanol-group-containing-polysiloxane solution after completion of polycondensation is not treated with the cation exchange resin.